This is not an authoritative guide. It
may not even be very accurate. I am just trying to lay things out as I
understand them, so as to try to sort out what I think I know and make some sort
of record of what I think I have learnt, before I forget everything and get
myself too muddled. I shall no doubt have to re-visit this page and make
corrections, from time to time.

Pre-clocks

Long before the earliest clock that we know of, people
tracked the passage of time. And if we believe that neolithic structures such as
Stone Henge were deliberately constructed so as to align to celestial events,
then our ancestors appear to have been able to track the passage of time with
considerable accuracy. We can only guess at the lengths to which our ancestors
went, but it is clear that the act of tracking and measuring time has long been of
very great importance to mankind.

Clocks

At some point in the depths of time, a clock was
invented. The science of horology is the pursuit of ever more precise and
dependable measurements of time. At least, that's what the word truly means. For
a long time, horology has also encompassed the decoration and elaboration of
timepieces. A viable, functional, dependable clock was, after all, an
achievement worth boasting about. By and large, however, it was the accuracy of
a clock that
defined a clock-maker's place in history.

Compared to the apparent pace of progress in our modern,
technological world, clocks seem to have taken ages to get anywhere. I'm no
expert on clocks (let's face it, I'm no expert on anything), but I have heard it
said that clocks of old could be very, very accurate. Pendulum mechanisms and
grasshopper escapements and all sorts of clever thinking could render a
mechanical clock as accurate as you'd likely ever need. Someone recently built a
'Longitude' clock from John Harrison's eighteenth century design and it
entered the Guinness Book of Records for losing only five eighths of a
second in a hundred days. That would work out at less than 2.3 seconds per year.

Watches

In a world already fast being shrunk by trade and conquest, the
ability to accurately navigate at sea would free ships from the need to sail
relatively close to shore.
Accurate navigation, and with it the ability to take more direct routes across
large tracts of open sea, depended on having a highly accurate and highly
consistent time-keeping device. But, transferring the accuracy of a large, stationary clock
into a small, mobile package was, apparently, an enormous challenge. Without a
pendulum and a rock-steady platform, the mechanism would need springs and a
design that would work no matter which way up it was or what forces of motion
were applied to it.

This isn't the place to try to lay down a history of
mechanical watches, so suffice it to say that a fairly wide variety of
escapement designs were tried and the one that came to dominate the modern world
of wristwatches - the Swiss lever escapement - was not necessarily the most
accurate, but did display good accuracy, robustness and reliability that gave it
the competitive edge.

Wristwatches

Today, the Swiss lever escapement is found in almost every
mechanical watch from every major watch producer except for Omega. Small,
independent brands occasionally come up with something new. Top, high-end brands
occasionally come up with an interesting prototype or an unbelievably expensive
limited run of watches that incorporate something other than a Swiss lever
escapement. But the industry, from small players to large, is locked into this
one particular movement. And pretty much for the same reasons that led to the
Swiss lever escapement's rise to popularity several hundred years ago - it's
reasonably accurate, sturdy and dependable.

Reasonably accurate... Therein lies the 'tell'. The
statement that reveals that the core focus of the majority of watch-makers has
shifted, inescapably and irreversibly, away from true horology. Two or three
seconds per day is accurate enough. You can't compete with quartz, so there's
little point trying to push the 'accuracy' angle. Better focus on design,
complications, craftsmanship. Better sell it like it's jewellery. There are
mechanical watches, now, with
moonphases so accurate that it will be over two million years before they are
off by as much as a day. But they still can't promise to keep time to better
than a couple of seconds per day and any fancy new developments that may from
time to time emerge in making mechanical watches more accurate, are all rather
like trying to squeeze one or two extra miles per hour out of a steam train.

So, I won't dwell on the modern mechanical watch for very
long, but I will mention some notable developments that have contributed to
making today's clock-work watches better time-keepers than their predecessors.

Escapements

Omega's version of the Daniels co-axial escapement was
not intended to deliver greater accuracy than a Swiss lever escapement, but to
reduce wear and to improve longevity of the movement and consistency of
function. With the move to silicon balance springs in their Master Co-axial
version of the escapement, Omega have raised the game a notch. Rolex have moved
to using Parachrom hairsprings and Paraflex shock absorbers to make movements
that are both strongly resistant to the effects of shock and magnetism and that
deliver more consistent performance over time. Sinn's Diapal approach removes
the need for oil in the escapement, and in so doing removes one of the key
maintenance areas of any mechanical watch.

Not more accurate, then, but more reliable and more
consistent. And that is a key component of a high accuracy watch. There is no
point in having the world's most accurate movement if it can maintain that
accuracy for only a week before needing to be serviced.

Beat rates

One thing that used to signify a high-maintenance watch
was a high beat rate. Modern lubricants, new alloys and very high precision
engineering have made it easier to produce reliable high beat movements. Once
considered to be 'high beat', 28,800 bph movements are now rather common. So,
why choose a higher beat rate anyway? Smaller, faster-rotating balance wheels
are said to be harder to disturb than larger, slower wheels, and this reduction
in sensitivity to external mechanical forces is believed to give high beat
movements the advantage in maintaining accuracy.

36,000 bph is considered 'high beat', today, although
there have been movements with much higher beat rates than that. Grand Seiko is
particularly well-known for 36,000 bph movements, but they also produced a
less-well-known 43,200 bph movement under the 'Credor' brand in 1998 (the
GBBX998).

Electric watches

Many years earlier, Citizen had also produced a 43,200
bph watch in their 'Cosmotron' line of electric watches. Electric watches date
back to a time before quartz, when watch-makers still vied to create the most
accurate timepieces possible. Starting with Hamilton, in America, electric
watches began to emerge in the late 1950s but although they are seen as an
important development in wristwatch technology, the addition of an electrical
drive unit did nothing, by and large, for the accuracy of the movements.

Tuning forks

Tuning forks, however, were a whole new ball game. Coming
not so long after the advent of the Hamilton Electric 500, Bulova released the
world's first tuning fork watch in October, 1960. The wristwatch's beat rate had
suddenly shot up to 360 Hz as a metal tuinng fork was vibrated under the
influence of electromagnetic impulses. Those vibrations were translated directly
into drive for the hands, resulting in an incredibly smooth progression of the
second hand around the dial. Adjusting the rate of the watch was achieved by
adjusting the balance of the tuning fork. Aesthetics of a smooth-gliding second
hand aside, the tuning fork watch claimed to be able to deliver accuracy of a
minute per month and with that claim it blew every other type of watch out of
the water for the next decade.

Several manufacturers jumped onto the tuning fork
band-wagon, and different movements featured 300 Hz, 360 Hz and 720 Hz
oscillators. Omega's 720 Hz Megasonic was released in 1973 - well into the
quartz era and just one year before the company released their 2.4 MHz quartz
Marine Chronometer. In fact, both tuning fork and electric watches continued to
be produced by several companies right through the early years of quartz.

Quartz

When quartz watches came along, it wasn't as if the game
was over and all other types of watches ceased to be produced. The earliest
quartz watches were incredibly expensive and somewhat delicate. They had been developed, however,
because it was seen how good larger quartz clocks were and bringing such
accuracy to a wristwatch was an obvious and logical step. From a piece of metal
vibrating at several hundred hertz, the horological world moved on to quartz
crystals vibrating at several kilohertz. Today's standard quartz frequency is,
of course, 32 kHz, but this was not the case in the beginning.

Frequencies

The first quartz watch on the market in 1969 (the Seiko
Astron 35SQ) had an oscillator frequency of 8 kHz (8,192 Hz). A month later, in
January 1970, Seiko released an updated version with a 16 kHz (16,384 Hz)
oscillator. Later the same year, Omega became the first Swiss watchmaker to
release a quartz watch, with its iconic Electroquartz being the first to feature
the CEH consortium's Beta 21 movement (re-packaged as Omega's cal. 1300), which
also used an 8 kHz oscillator.

In 1971, Seiko launched the V.F.A. 38SQW. Besides the
frequency of the oscillator, this may be
considered to be the first quartz watch to exhibit all the features that you
will find in today's timepieces. As with the updated 35SQ, the 38SQW used a 16
kHz oscillator, cementing Seiko's move away from 8 kHz movements. Not far behind
Seiko, Girard Perregaux released the cal. 350 which also featured all the
various attributes of modern quartz watches and upped the game a notch by
sporting the world's first 32 kHz (32,768 Hz) oscillator.

Meanwhile, through the continued run-out of
the CEH group's Beta 21 movement, 8 kHz oscillators continued to come to market
in watches by Rolex, Zenith, IWC, JLC, Longines, Rado, Bucherer, Bulova, Piaget
and Patek Philippe. With GP the only one to feature a 32 kHz oscillator, and
Seiko doing their own thing with 16 kHz, it was by no means clear, in the first
couple of years of the 1970s, that 8 kHz watches were living on borrowed time.
By 1975, however, oscillator frequencies had hit an all time high.

Let's remember that in 1973 Omega were still releasing
tuning fork watches. Quartz was not yet the only player in town. But regardless
of the innards, it was clear that (in some quarters of the watchmaking world, at
least) there was a focus on developing higher frequency movements. Omega's 1973
Megasonic took tuning fork movements to an unprecedented 720 Hz, and in 1974 the
same company released the world's first quartz watch with an oscillator in the
MHz range - the 2.4 MHz Omega Marine Chronometer. Wristwatch accuracy was now
rated to just one second per month. In Japan, Citizen was also
working on a high frequency quartz oscillator and in 1975 they released the
Crystron 4 Mega, sporting a 4.19 MHz oscillator. The boast, at the time, was
that the 4 Mega would hold to three seconds per year. Only
very, very recently, with the advent of atomic watches and self-calibrating
thermocompensated movements has any manufacturer promised a tighter spec. than
that.

By the late 70s, electric and tuning fork watches were
out, and quartz was in. But approaches to improving accuracy were still far from
settled. Citizen continued to produce 4 MHz watches for several years, and
Junghans jumped on this band-wagon in 1978, with Casio following suit in 1980.
But by that time, things had moved on. In 1977, a year before Junghans released
their MegaQuarz, Rolex brought to market the world's first movement to feature
both rate adjustment and thermocompensation (the Oysterquartz cal. 5035).

As immune as they may be to the vagaries of motion and of
gravity, quartz crystals nevertheless face a very significant challenge to their
ability to maintain a steady rate of oscillation and that, of course, is temperature. The frequency at
which a quartz crystal oscillates, at a given voltage, varies depending on its
temperature. Up until 1977, most quartz watches were simply treated to fine rate
adjustment at a set temperature in the factory. With a little patience, a very
finely adjusted movement could probably be relied upon to keep to within a few
seconds each month. This was far better than any mechanical or tuning fork could
promise, and may well have been more accurate than most people would have
considered necessary. The trouble is, that even a very finely adjusted movement
could only deliver consistent high accuracy performance if it was treated to
consistent, fairly narrowly-defined climatic exposure.

By using high frequency oscillators, Omega, Citizen,
Junghans and Casio had sought to create movements that were simply less
sensitive to temperature fluctuations. The high frequency approach, however, had
its drawbacks. The most obvious problem with using a MHz-range oscillator would,
of course, be battery life. Beyond the practical considerations, however, I also
think there may have been a sense that high frequency movements were a bit
stuck-in-the-past. Besides the higher frequency oscillator, these movements were
much like any other of the mid-70s and did not reflect the pace of change in the
world of microelectronics. Even Casio's digital 4 MHz watch was nothing
particularly new. Digital watches had been around for years, and Casio's high
accuracy offering in 1980 was both too late to capitalise on the high frequency
band-wagon, and too expensive for what was, in all other respects, a rather
ordinary timepiece.

In 1977, Rolex redefined 'state-of-the-art' in quartz
watches, with the release of the Oysterquartz and the world's first movement to
feature both a rate trimmer and thermocompensation. Without suffering the same
impact on battery life as MHz watches had seen, the Oysterquartz could deliver
consistent high accuracy regardless of changes in climatic conditions. It did
this by measuring the one variable that it couldn't adjust - the temperature -
and adjusting the one variable that it could - the current supplied to the
oscillator. In this way, the counting circuitry simply had to keep counting a
steady 32 kHz oscillation, while the current fed to the oscillator was varied by
comparing its temperature (as measured by a nearby thermistor) against a record
of its pre-established thermal performace. And if you're surprised to learn that
Rolex was once producing the world's most advance quartz watch, you may be even
more surprised to learn that they once even developed
an LED watch.

Today, it is suspected that Citizen and possibly also
Seiko use the VCTCXO approach (or perhaps some variation on the theme), although
their precise methods are not clearly documented.

Twin quartz & dual oscillator

In 1978, Seiko's response to the advent of
thermocompensation was their Twin Quartz range. Seiko's approach differed from
Rolex's in two ways. First, instead of using a thermistor to measure the
temperature, Seiko used a second quartz oscillator. Second, instead of adjusting
the frequency of the oscillator, Seiko adjusted the count.

It is not 100% clear from the documentation, but it
appears that some Twin Quartz movements may have employed two oscillators of the
same (32 kHz) frequency. The idea seems to be that these oscillators are somehow
slightly different and have different thermal performances. This being the case,
the frequencies of the two oscillators will change at different rates, as the
temperature rises (or falls). By measuring the difference between these two
rates, the movement's circuitry can determine the temperature which the
oscillators are experiencing. Once the temperature is known, the movement's
circuitry compares it to the pre-established thermal performance of the main
oscillator, and instructs the count circuitry to deduct an appropriate value.
For example, the frequency of a slightly cool oscillator may not be 32,768 Hz,
but, say, 32,780 Hz, in which case the count circuitry should be instructed to
deduct '12' from its count. The count circuitry then sends a pulse to the
stepper motor to move the hands at pretty much exactly the right time.

Now, having just given that example, I am very conscious
that the numbers are likely to be way off the mark. There are aspects of the
mathematics of quartz watches on which I am simply not up-to-speed. It could be
that such small changes cannot be adjusted for due to the way in which count is
divided (remember, a count of 32,768 must be divided down to just one tick per
second). But anyway, I think the basic idea, as I have presented it, is sound.

Even if some of Seiko's Twin Quartz movements may have used
two 32 kHz oscillators, others clearly did not. The 9442 draws half a microamp more power
than the 9923, using the same battery (ref.
Seiko Battery List). While the 9923's
documentation is less than 100% clear about the frequency of the auxiliary
oscillator, the
documentation of the 9442 clearly states that the auxiliary
oscillator for that movement has a frequency of 40 kHz (40,960 Hz). The
documentation for the 10 SPY cal. 9943 and the 5 SPY cal.
9983 is missing, but the power consumption and
battery life for these two movementts are almost identical to those of the 9923. So, on the balance of
probability, I believe that the 9943 and 9983 most likely have 40 kHz auxiliary oscillators. The use of a higher frequency
auxiliary oscillator no doubt has a direct impact on battery life, but it may offer more accurate
temperature measurement.

It is clear that Seiko's approach produced watches that
were far more accurate and far cheaper than Rolex's Oysterquartz, but I believe
there was a fundamental flaw in the Twin Quartz concept: crystal ageing. As a
crystal oscillator ages, its thermal performance changes. If your watch has a
rate trimmer, then you can adjust for this. But if the accuracy of your watch
depends on knowing the thermal performance of not one but two crystal
oscillators, then you're in trouble. On the circuitry of each Twin Quartz
movement are two trimmers: one for the main oscillator and another for the
auxiliary. Seiko's technical manuals advise those servicing Twin Quartz watches
to touch only the trimmer of the main oscillator and under no circumstances to
touch the other! The intrepid watch-fixer is further advised that, prior to
attempting regulation, he should use a Seiko QT-99 to determine the rate of the
watch. If its rate falls outside of a reasonable range, then replacing
components, rather than regulation, is advised. To me, the message is clear: the
second oscillator is a problem, and once it has drifted too far off the mark,
efforts to trim the rate via the main oscillator are futile. The best you could
hope for is to bring the watch back to delivering a good rate at a given
temperature. But once the effects of ageing have truly taken their toll, the
circuitry is going to be applying all sorts of erroneous count 'corrections'
every time the temperature rises or falls. So, unless you keep your watch in a
temperature-controlled oven, you have no hope of seeing the original factory SPY
values again.

So, that settles it, then. Thermistors are the way to go.
Except... the watch that is currently performing best in my collection is a dual
oscillator Longines. Most of what I know about this, comes from
one
particular thread on the WUS HAQ forum, which would date ETA's dual
oscillator movement to the late 1980s. I believe Seiko had given up on Twin
Quartz watches by the mid-80s, and as far as I can tell, ETA didn't stick with
the concept for very long. So, how come the Longines is keeping such fantastic
time when my amazing cal. 9983 Seiko SQ has slipped from its 5 SPY factory spec.
to 271 SPY, today? The Longines may well have had its rate adjusted over the
years, whilst the Seiko may not have been adjusted at all, and the conditions in
which each has been kept over the decades may also have influenced their
performance. But I believe there's something more.

When I put any of my Seiko Twin Quartz watches on a
Witschi QT-3000 (on the side that takes a rate from a measurement of the
oscillator frequency), the displayed rate fluctuates constantly. This is what you'd expect
with two oscillators continuously putting out conflicting frequencies. The
Longines, however, returns a nice, steady rate, except for periodic
fluctuations. To me, this suggests that the approach taken by ETA differed from
that taken by Seiko. The Seiko Twin Quartz movements have no inhibition periods.
They constantly adjust for temperature changes as the measured difference
between oscillator frequencies changes. Service manuals advise that the Twin
Quartz watches cannot be timed on a QT-99 using any of the standard 'gate'
timings, but have to be timed on an open setting and with the stem pulled out to
stop the auxiliary oscillator. I believe ETA's dual oscillator movement has the
auxiliary oscillator kick-in only once in each inhibition period. I believe this
idea is further supported (beyond the results from the timing machine, that is)
by the fact that the battery life of the dual 32 kHz Seikos is three years,
while the battery life for the variants wielding both 32 kHz and 40 kHz
oscillators shrinks to two years on the same battery. The ETA movement is said to use a 262 kHz oscillator as its
auxiliary, and it sports a battery of similar size to that used in the Seikos.
Honestly, you don't have to be an electrical engineer to see that the ETA would
run out of juice in pretty short order if both oscillators were running
all the time.

The effect of using a much higher frequency oscillator
would be a more accurate temperature calculation. The effect of switching it on
only once per inhibition cycle would be both to conserve batter life but also to
reduce the effect of crystal ageing. The ageing of the Seikos' auxiliary
oscillators would occur far more quickly than would be the case in ETA's
movement, resulting in a speedier decline in the maximum achievable SPY value
for the Japanese movements. So, while Seiko's Twin Quartz watches struggle to
stay on spec., today, my dual oscillator Longines sits comfortably at the top of
my performance chart.

Digital count adjustment

Thought to be the basis for all modern thermocompensated movements
from ETA, digital count deduction is based on the cross-referencing of
measured temperature against thermal performance data. It is also broadly
assumed that all top, modern movements (from any and all manufacturers) use just one crystal oscillator and that
that oscillator has a frequency of 32 kHz. It is worth reiterating, however,
that, for the most part, we just don't know this for sure.

When I put a DS-2 on a heater and observe the rise and
fall of its rate, the
thing flat-lines at 50 degrees centigrade (that is to say, the rate ceases to
rise and fall and just becomes completely steady), possibly lending weight to the idea
commonly mooted in HAQ circles that TC movements may deduct count but not add
count. But then there's the DeHavilland watch whose creator told me that count
can be both subtracted and added, in
his product. I have read, somewhere, that
Citizen have claimed not to use TC at all, but I haven't seen anything directly
from Citizen in that vein and I think it is simply beyond belief in HAQ circles
that a 5 SPY watch could promise such accuracy without employing some method to
combat the problem of changing temperatures. We know they once did it with
MHz-range oscillators, but we're fairly sure those days are behind us. We're on slightly surer ground with
ETA, but even the apparently open Seiko is shrouded in a bit of mystery. Do they
use count deduction and is it digital or analogue?
Prevailing wisdom says they do use count deduction and that it is 'digital', but
bloggers and
senior members of Japanese watch fora are somewhat insistent that Seiko use
an analogue method (and some even suggest that count deduction might well be a
technology that the Swiss have entirely to themselves).

Radio and GPS and other synchronised options

Junghans were the first to come out with a wristwatch
that could synchronise its time with the radio signal from an atomic reference
clock. Often called 'radio-controlled' watches in the UK, and 'atomic' watches
in the US, these watches tend to have no greater inherent accuracy than an
ordinary quartz watch. They may boast of 'atomic' level accuracy and not losing
a second in ten thousand years, but in reality any of my newer HAQ watches will
almost certainly lose less time in a month than an RC watch will lose over the
course of a day. The watch may have showed the correct time when it sync'd at 2
a.m., but by tea time you really would have no idea what the precise time was.
And no, you can't just be blithely dismissive of the importance of that second.
Not when the very boast of the watch is that it has '1 second per 10,000 years'
accuracy.

Much the same thing is true of GPS-sync'd watches. Seiko
may have brought GPS to the wristwatch, but Citizen seem to be the only ones to
have done anything to improve the un-sync'd accuracy of their GPS range of
watches, with their F900 holding 5 SPM in the absence of satellite data. Apple
may have boasted that their watch is accurate a second in ten thousand years (or
whatever it was that they said), but again this relies on the watch getting its
time signal from the 'phone which, in turn, gets its time signal from a
broadcast atomic reference. Disconnect these devices and their time-keeping
falls back to the levels of the earliest quartz watches (or worse).

MorgenWerk have released a series of watches that are
GPS-sync'd and also boast self-learning TC to provide an un-sync'd rate of
0.75 SPY, and Hoptroff have an internet-sync'd watch that promises 1 SPY in
much the same way, but if you have never heard of these companies then you are
not alone. This is not mainstream technology by any stretch of the imagination.
Logically, it's the direction in which horology should be moving. Xonix tried a
similar approach with watches that could synch via a web app and trim their own
rate as necessary, according to accumulated data. Some implementations of the
technology
were found to work, while others were not. These cheap-and-cheerful watches
lacked thermocompensation, but they showed what ought to be possible. Now that
we have both Hoptroff's and MorgenWerk's versions of this self-calibrating
technology in thermocompensated watches, we are finally starting to see real
evolution in precision time-keeping. But let's not lose sight of the fact that
these two, small companies do not necessarily mark the beginning of a sea change
in the industry. Unless their technologies are taken up by one or more of the
big manufacturers, it's hard to say that the world of high accuracy watches has
really moved on.

Atomics

Both Hoptroff's smartwatch and MorgenWerk's GPS watch may
struggle to justify their existence as both smartwaches and GPS watches are
already widely advertised as being dead-on accurate all the time. Only those who
really pay attention will notice that they aren't, and maybe even fewer will
really care that much. As long as a connected watch or a GPS watch syncs from
time to time, it's probably ok for most users. It's an uncertain time for the
horological hopeful. But these self-calibrating, thermocompensated, 1 SPY
watches are not the only fledgling technologies hoping to secure footholds in the
market. Hoptroff also has
atomic watches.

Not 'atomic' like what some people call those
radio-sync'd watches, but watches with small atomic clocks inside. In low power
mode they can offer accuracy of 1 second per hundred years. In full power mode,
that goes up to 1 second per thousand years. The size and cost would no doubt
rule out these watches for most consumers, even if they had even heard of their
existence. Definitely as accurate as a watch could hope to be, but, as with the
other offerings from Hoptroff and Morgenwerk, not game-changers just yet.

And so, here we are. In 45+ years of quartz watches, is
this as far as we have come? Thermistors and digital count correction? 5 to 10
seconds per year? We had that in 1978! Are quartz manufacturers now giving up on
the pursuit of ever more accurate timepieces and following the path trodden by
makers of mechanical watches, refocusing their efforts on complications and
design features? Citizen, Seiko and ETA continue to develop and produce new high
accuracy quartz movements, but they are all still rigidly spec'd to 5 or 10 SPY.
I have the self-learning, thermocompensated watches of Morgenwerk and Hoptroff
and I am considering saving up for
one of Hoptroff's atomics, too, but these are niche players and, in all honesty,
I'm not particularly confident that they will still be around, ten years from
now.